Fuling Shale Gas Research Articles

Shale pore pressure seismic prediction based on the Hydrogen generation and compaction-based rock physics model and Bayesian Hamiltonian Monte Carlo inversion method

The seismic prediction of formation pore pressure is critically important for the exploration and appraisal of shale oil and gas reservoirs, as well as for identifying optimal drilling targets within these formations. In particular, the complex pressure regimes of deep shale reservoirs introduce substantial challenges to traditional seismic prediction methodologies. A Bayesian Hamiltonian Monte Carlo pre-stack seismic inversion approach is proposed to enhance the accuracy of pore pressure estimations based on an advanced rock physics model that integrates compaction and hydrocarbon generation effects. Initially, a comprehensive petrophysical model is developed to account for the effects of hydrocarbon generation and compaction, establishing a robust framework for the normal compaction trend simulation. Subsequently, a novel formation pressure prediction model is derived based on integrating the Eaton model and the Bower stress hypothesis. Then, the Bayesian HMC seismic inversion method is proposed to predict formation pore pressure in shale reservoirs with elastic impedance data set. The proposed methodology is validated through application to actual well log and seismic data from the Fuling shale oil and gas reservoirs in the Sichuan Basin, which demonstrates significant potential of this method for enhancing the prediction of pore pressure in complex geological settings.

Integrated AutoML-based framework for optimizing shale gas production: a case study of the Fuling shale gas field

Integrated AutoML-based framework for optimizing shale gas production: a case study of the Fuling shale gas field

Greater environmental risk of shale gas produced water from lacustrine than marine sources in Fuling shale gas field, China: Insights from inorganic compounds, dissolved organic matter, and halogenated organic compounds

Lacustrine shale gas represents a promising frontier in the future development of shale gas resources. However, research on the characterization of lacustrine shale gas produced water (SGPW) remains scarce. In this study, we characterized the geochemical properties of both marine and lacustrine SGPW (MSGPW and LSGPW) and assessed their dissolved organic matter (DOM) components using fluorescence EEM spectroscopy. Additionally, we employed Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to analyze halogenated organic compounds (HOCs) and non-HOCs in SGPW, as well as their transformations during storage in open impoundments. Pollutants in LSGPW generally had higher concentrations and greater fluctuations compared to those in MSGPW. Our findings from EEM spectroscopy and FT-ICR MS revealed that phenolic compounds may be important components of DOM in all SGPW. Moreover, the number of detected unique molecules in LSGPW was greater than in MSGPW. CHO or CHOS compounds dominated in non-HOCs, with LSGPW exhibiting generally higher DBE, modified aromaticity index (AImod), nominal oxidation state of carbon (NOSC), double bond equivalent minus oxygen per carbon ((DBE-O)/C) values, and lower H/C values compared to MSGPW, while unsaturated aliphatic compounds typically dominated in HOCs. Furthermore, we employed 37 transformation reactions that might occur during SGPW storage and found that oxygen addition and dealkyl group reactions were predominant, with these two types of reactions occurring more frequently in LSGPW than in MSGPW. LSGPW exhibited higher toxicity compared to MSGPW, with toxicity positively correlated with the concentrations of inorganic salts and organic substances with higher AImod, NOSC, and (DBE-O)/C. These findings contribute to a more comprehensive understanding of LSGPW, enabling the design and implementation of more rational disposal measures to effectively mitigate its potential environmental risks.

A comprehensive logging evaluation method for identifying high-quality shale gas reservoirs based on multifractal spectra analysis

Conventional logging interpretation methods qualitatively identify shale reservoirs using shale attribute parameters and interpretation templates. However, improving the identification accuracy of complex shale reservoirs is challenging due to the numerous evaluation parameters and the complexity of model calculations. To quantitatively characterize high-quality shale reservoirs effectively, this study utilizes two wells in the Fuling shale gas field as examples and establishes a comprehensive evaluation method for identifying high-quality shale gas reservoirs utilizing multi-fractal spectral analysis of well logs. First, the conventional well logs are qualitatively analyzed and evaluated via multiple fractals and R/S analysis. Subsequently, a gray relational analysis is employed to combine the production well logging, which reflects dimensionless productivity contributions, with the fractal characteristics of conventional well logs to obtain the corrected weight multifractal spectrum width ∆α' and fractal dimension D’. Comprehensive fractal evaluation indices λ and γ are introduced, forming three categories of productivity evaluation standards for shale gas reservoirs characterized by fractals. Finally, a validation well is employed to demonstrate the effectiveness of the evaluation method. The results indicate that the identification of high-quality shale gas reservoirs based on the above comprehensive fractal evaluation method can reflect the productivity classification level of fractured well sections, simplify the calculation of formation evaluation parameters, and avoid the problem of poor correlation between predicted sweet spot zones and gas production. This approach has wide applicability and value for identifying high-quality reservoir areas in shale gas reservoirs and provides technical support for the effective large-scale development of shale reservoirs.

Contrasting fracturing and cementation timings during shale gas accumulation and preservation: An example from the Wufeng-Longmaxi shales in the Fuling shale gas field, Sichuan Basin, China

The marine shales in southern China are characterized by high thermal evolution and intensive deformation during multistage burial and uplift. Fracturing and cementation, associated with tectonic activity, diagenesis, hydrocarbon generation and migration processes, are widely and variably distributed in shale reservoirs experiencing different tectonic evolution. In this study, we utilized cross-cutting relationships, fluid inclusion microthermometry, and laser Raman spectroscopy of fluid inclusions, along with U-Pb dating of fracture-filling calcite veins, integrated with burial history modeling, to elucidate the timing and mechanism of fracturing in the Paleozoic Wufeng-Longmaxi shale reservoir, as well as regional variations in the Fuling shale gas field. Bedding-parallel fractures (BFs) in shale reservoirs are filled with calcite and quartz veins. The timing of fracturing, as determined by minimum homogenization temperatures and U-Pb dating, is estimated to have occurred during ca. 191 -122 Ma, during which some short vertical (or high-angle) fractures (VFs) opened around 163.4 Ma and 137 Ma, subsequently sealed by calcite veins, respectively. All calcite and quartz veins within these fractures contain high-density methane inclusions, while shale reservoirs were in a high-over-mature evolutionary stage. This suggests that fracturing was primarily driven by gas generation overpressure during deep burial. In shale reservoirs near fault belt folds, multistage fractures developed, including three stages of intersecting fractures (IFs) and one-stage of long VFs. The timing of fracturing and cementation corresponds to the Yanshanian tectonic uplift (ca. 83 - 69 Ma) with intense tectonic movement likely being the direct cause of fracture opening. The presence of abundant gas inclusions in veins recorded shale gas expulsion during rapid tectonic uplift, reflecting the destruction of shale gas preservation conditions. In contrast, no significant fracturing or cementation processes have been observed in the tectonically gentle zones. The different fracturing and cementation processes indicated that preservation conditions declined with increased fracture openings during uplift, correlating with the gas enrichment.

Novel method for total organic carbon content prediction based on non-equigap multivariable grey model

Predicting total organic carbon content plays a crucial role in shale gas reservoir evaluation. To address multi-variable, imperfect logging data and non-equigap characteristics, this study developed a multi-variable grey derivative model for predicting the total organic carbon content trend. To begin with, the non-equigap factor is introduced and the parameter identification of the new model is established on the basis of least square method. Then, to reduce fluctuations in the original data, the weighted geometric average weakening operator is introduced. In addition, considering the system stability, the derivation method is used to calculate the time response formula of the model. Furthermore, two validation cases are provided to verify the validity of this novel model. Finally, the model is applied to the Fuling shale gas field in China for practical forecasting. Compared to other models, such as the grey model, statistical model, and artificial intelligence model, the proposed model achieved higher prediction accuracy in the three cases. Specifically, this model obtained 95.62%, 95.88% and 94.55% prediction accuracy for total organic carbon content. Results that the new model effectively addresses the limitations of previous studies that focus on single-parameter or equal spacing issues.

Study on fracturing fluid return pattern and production characteristics of shale gas wells

We innovatively propose a research method through micro-experiment + macro-measurement, combined with onsite proppant return test. This method can solve the problem of unclear impact of the return shut-in time, return rate control and return effect on production. We carried out a specific applied research for Fuling shale gas Jiangdong block, specifically determined the mineral composition, overburden pressure physical properties before and after fracturing fluid percolation, the changing law of resistance environment of gas production channel inside the reservoir before and after fracturing fluid percolation, and explored the settlement problem of proppant’s size, type and nature in the fracture through the situation of sand return. This study concludes that the reservoir testing process can be divided into pure fluid production stage, gas breakthrough stage, and stable production stage. The optimal contact time between shale and fracturing fluid promotes the hydration of clay minerals to produce microfractures and the formation of a complex network of intercommunicating seams facilitated by external dynamics, which promotes gas production. And the wrong return after fracturing will affect the hydraulic fracture conductivity.

New approach of evaluating fracturing interference based on wellhead pressure monitoring data: a case study from the well group-A of Fuling shale gas field

Well pattern infilling has become an effective means for improving the development effect of gas reservoirs in unconventional gas reservoirs. The hydraulic fracturing of infill wells causes widespread fracturing interference between new and old wells. Because fracturing interference has a significant influence on the production of old wells, it is urgent to evaluate the degree of fracturing interference. This paper proposes a new approach to evaluating fracturing interference between new and old wells, which is based on a systematic analysis of the variation pattern of old well wellhead fracturing during the fracturing process of new wells. This new approach not only provides a semi-quantitative evaluation for the degree of fracturing interference between fracture sections of new and old wells but also achieves inter-well connectivity evaluation between new and old wells. This new approach is applied in well group A of the Fuling gas field to demonstrate its analysis process. The results show the different types of fracturing interference result in different levels of pressure response between each fracturing section and the old wells. For example, The pressure rise of old well A7-1 is more obvious in the fracturing process of the 2nd, 14th, and 13th sections of new well A68-5, and the old well A7-2 has significant fracturing interference with the 1st, 2nd, 3rd, 4th, and 6th sections. This achieves a semi-quantitative characterization of fracturing interference between new and old wells. The degree of fracturing interference between the old well A7-2 and the new well A68-5 is the strongest in well group A, which is the effect of compression fracture interference. The old wells A7-3 and A15-3 are the least impacted by fracturing interference, and follow the old wells A15-2 and A7-1. This result has implications for assessing the degree of fracturing interference and inter-well connectivity in unconventional gas reservoirs.

Study of fracturing fluid re-discharge based on percolation experiments and sampling tests – An example of Fuling shale gas Jiangdong block, China

Abstract Shale gas development requires the use of hydraulic fracturing, and the relationship between fracturing fluid drainage and production is not clear. Therefore, it is necessary to adopt the method of core experiment combined with engineering validation to achieve the description of the seepage-absorption-return mechanism of shale and to optimize the selection of fracturing fluids and the testing work system in engineering. In this study, a “seepage experiment → sampling test → engineering validation” working procedure is proposed, and it is found that seepage occurs only on the surface of the fracture where the liquid medium intrudes into the fracture and that the amount of water absorbed is directly proportional to the area of seepage; the rate of return is inversely proportional to the production rate in the same secondary tectonic unit; and the absorption rate per unit area of four types of cores with the same surface area is directly proportional to the yield of the fractured shale in the same medium. Under the premise of the same medium, the water absorption per unit area of the four types of cores varies with the rate of change with time, but the general trend is the same. Under the premise of different secondary tectonic units, when the time of good closure is similar, the correlation between the return rate and the test production is weak.

Feasibility of hydrogen storage in depleted shale gas reservoir: A numerical investigation

Due to the low operation cost, high containment security, and large storage capacity, depleted shale gas reservoirs are considered as promising options for large-scale hydrogen storage. However, its feasibility has not been systematically examined yet. It is still unknown about whether the deliverability (injection/withdrawal) capacity could meet the energy supply/demand and how the depletion time, cushion gas selection, injection/withdrawal strategy will influence the performance of this scenario.Therefore, we present a numerical compositional modelling investigation on hydrogen storage in a partially depleted Fuling shale gas reservoir in China. The results demonstrated that: 1) a high injection/withdrawal capacity could be achieved through a single shale play pad in the area of interest as approximately 5.4 × 108 Sm3 hydrogen could be stored and 3 × 108 Sm3 could be recovered in each cycle (equal to 0.54 TWh of power output). 2) CH4 production is inhibited once hydrogen storage project is performed, an early depletion time could significantly reduce CH4 production but slightly improve H2 withdrawal. 3) Cushion gas injection is beneficial to reducing H2 loss and enhancing 2.8% H2 recovery, while the main drawback of this operational measure is an increase in capital cost in gas separation due to lower H2 purity in the produced gas.This work demonstrates that shale gas reservoir is a promising candidate for hydrogen storage, which is beneficial to the implementation of large-scale hydrogen economy and the operation of hydrogen supply chain.

Noise Characteristics and Denoising Methods of Long-Offset Transient Electromagnetic Method

The advantages of the long-offset transient electromagnetic method include deep detection and sensitive response to resistivity anomalies. It is widely used in underground mineral resources exploration, fluid identification in petroleum reservoirs, hydraulic fracturing, and dynamic residual oil and gas monitoring. After the primary field signal is turned off, grounded electrodes or coils are used to observe the secondary eddy field. The secondary field signal decays quickly and has a large dynamic range and a wide frequency band but is easily affected by various natural and human electromagnetic interferences. Therefore, noise reduction and distortion correction are important issues in the processing of transient electromagnetic data. This paper proposes a systematic noise interference suppression process. Multi-period and positive–negative bipolar signal stackings were used to remove random noise and suppress DC offset signals. Then, a time-domain inverse digital recursive method was applied to remove characteristic frequency signals, e.g., power frequency signals and their harmonic interference. A standard noise-free signal was constructed through forward modeling simulation and verified by adding different types of noise. Finally, high-quality transient electromagnetic secondary field attenuation signals were obtained through overlapping windowing technology. We applied this algorithm to obtain electromagnetic data from dynamic monitoring of hydraulic fracturing in Fuling shale gas and from a copper–iron metal mine in Daye City, demonstrating its effectiveness.

Theory, technology and practice of shale gas three-dimensional development: A case study of Fuling shale gas field in Sichuan Basin, SW China

In the Jiaoshiba block of the Fuling shale gas field, the employed reserves and recovery factor by primary well pattern are low, no obvious barrier is found in the development layer series, and layered development is difficult. Based on the understanding of the main factors controlling shale gas enrichment and high production, the theory and technology of shale gas three-dimensional development, such as fine description and modeling of shale gas reservoir, optimization of three-dimensional development strategy, highly efficient drilling with dense well pattern, precision fracturing and real-time control, are discussed. Three-dimensional development refers to the application of optimal and fast drilling and volume fracturing technologies, depending upon the sedimentary characteristics, reservoir characteristics and sweet spot distribution of shale gas, to form “artificial gas reservoir” in a multidimensional space, so as to maximize the employed reserves, recovery factor and yield rate of shale gas development. In the research on shale gas three-dimensional development, the geological + engineering sweet spot description is fundamental, the collaborative optimization of natural fractures and artificial fractures is critical, and the improvement of speed and efficiency in drilling and fracturing engineering is the guarantee. Through the implementation of three-dimensional development, the overall recovery factor in the Jiaoshiba block has increased from 12.6% to 23.3%, providing an important support for the continuous and stable production of the Fuling shale gas field.

Graphic Template Establishment and Productivity Evaluation Model of Post-Fracturing Based on the Fluctuation Pattern of G-Function Curve

In the process of fracturing construction in shale gas reservoirs, microseism is a common means and effective method to evaluate the fracturing effect, but it is not suitable for large-scale and large batches due to its high applicability conditions and cost. Therefore, a concise, fast and low-cost post-fracturing effect evaluation method is needed to evaluate the complexity of fractures formed by fracturing in shale gas reservoirs. In this paper, based on the basic theory of the G-function, the free variable μ was introduced to correct the filter loss coefficient with the participation of natural fractures, and thousands of G-function curves were plotted with fracturing data from hundreds of gas wells in the southern Fuling shale gas field in China. Through the feature analysis of the curve morphology, a G-function graphic template conforming to the block was established, which contains four types and eight morphologies. Four characteristic parameters in the G-function curve were selected to establish a productivity evaluation model for shale gas wells. Based on the validation results, it can be seen that the G-function graphic template and productivity evaluation model proposed by the author had a good correlation with the post-fracturing productivity of shale gas wells, which provided a fast, economical and accurate method for the post-fracturing effect evaluation and productivity evaluation of shale gas wells and can effectively provide feedback on the field fracturing effect and guide subsequent fracturing construction.

Depositional-diagenetic process and their implications for pore development of Wufeng-Longmaxi shales in the Jiangdong block, Fuling shale gas field, SW China

Depositional environment and diagenesis are important factors affecting pore characteristics, whereas how differential depositional and diagenetic processes affect pore development and preservation in shale remains controversial. In this study, based on geochemical analysis, low-temperature gas (including N2 and CO2) physisorption, core observation, thin section and field emission-scanning electron microscopy, the influences of various paleoenvironmental conditions and diagenetic pathways on pore development of the Wufeng and Longmaxi Formations are investigated. The results indicate that paleoenvironmental conditions determine primary mineral composition and content of organic matter, resulting in the various shale lithofacies. Subsequently, minerals in different shale lithofacies experienced various diagenetic events and evolution pathways, finally affecting pore generation and evaluation. Three system tracts, including transgressive systems tract (TST), early highstand systems tract (EHST) and late highstand systems tract (LHST) are identified in the Wufeng and Longmaxi Formations. Siliceous shale, mainly deposited in the TST, contains large amounts of biogenic authigenic quartz and abundant organic matter. Authigenic quartz aggregates effectively inhibit compaction and protect abundant pores. The contents of extrabasinal components increase during the EHST, while biogenic quartz and organic matter decrease to mainly develop mixed shale. Insufficient microcrystalline authentic quartz and high content of clay minerals lead to higher degree of compaction in mixed shale than siliceous shale, resulting in fewer residual pores. In contrast, clay minerals in clay-rich shale, deposited in the LHST, undergo strong compaction and illitization of smectite during diagenesis, resulting in strong deformation and loss of primary pores. As a result, higher amount of OM pores is generated and preserved in the organic-rich siliceous shales from the bottom of Wufeng and Longmaxi Formation, and gradually decreases in the mixed shale, while clay-rich shale in the upper section of the Longmaxi has the lowest amount of pore volume.

Hybrid data-driven framework for shale gas production performance analysis via game theory, machine learning, and optimization approaches

A comprehensive and precise analysis of shale gas production performance is crucial for evaluating resource potential, designing a field development plan, and making investment decisions. However, quantitative analysis can be challenging because production performance is dominated by the complex interaction among a series of geological and engineering factors. In fact, each factor can be viewed as a player who makes cooperative contributions to the production payoff within the constraints of physical laws and models. Inspired by the idea, we propose a hybrid data-driven analysis framework in this study, where the contributions of dominant factors are quantitatively evaluated, the productions are precisely forecasted, and the development optimization suggestions are comprehensively generated. More specifically, game theory and machine learning models are coupled to determine the dominating geological and engineering factors. The Shapley value with definite physical meaning is employed to quantitatively measure the effects of individual factors. A multi-model-fused stacked model is trained for production forecast, which provides the basis for derivative-free optimization algorithms to optimize the development plan. The complete workflow is validated with actual production data collected from the Fuling shale gas field, Sichuan Basin, China. The validation results show that the proposed procedure can draw rigorous conclusions with quantified evidence and thereby provide specific and reliable suggestions for development plan optimization. Comparing with traditional and experience-based approaches, the hybrid data-driven procedure is advanced in terms of both efficiency and accuracy.

Case Study: Successful Application of a Novel Gas Lift Valve in Low Pressure Wells in Fuling Shale Gas Field

The Fuling shale gas field is facing a rapid gas production decline due to heavy liquid loading issues. Given the condition that most wells are located at remote areas in the mountains, the traditional gas lift methods that require either fixed compressor or skid-mounted gas lift trucks do not seem feasible and occur high operation costs. A new type of gas lift valve that can be opened or closed at a low valve dome pressure indicates the high sensitivity to low production pressure. Thus, the piping line pressure can be utilized to activate the valve due to its new advantages. In addition, the specially designed structure of the gas lift valve can be activated via pressure increases in the tubing to create a channel between the tubing and annulus. The valve that previously functioned as a dummy valve was then switched to a gas lift valve. Field application results show that all wells were successfully restarted by only utilizing the low piping pressure, and loaded liquid was lifted with gas production at an incremental rate that reached up to 27.4 × 10 kscm/d per well. Fewer slickline operations were conducted to replace the dummy valve. The result of the application shows that the new type of gas lift system has a wide range of application prospect for low pressure wells, especially for shale gas wells.

The generalized method for estimating reserves of shale gas and coalbed methane reservoirs based on material balance equation

As the main unconventional natural gas reservoirs, shale gas reservoirs and coalbed methane (CBM) reservoirs belong to adsorptive gas reservoirs, i.e., gas reservoirs containing adsorbed gas. Shale gas and CBM reservoirs usually have the characteristics of rich adsorbed gas and obvious dynamic changes of porosity and permeability. A generalized material balance equation and the corresponding reserve evaluation method considering all the mechanisms for both shale gas reservoirs and CBM reservoirs are necessary. In this work, a generalized material balance equation (GMBE) considering the effects of critical desorption pressure, stress sensitivity, matrix shrinkage, water production, water influx, and solubility of natural gas in water is established. Then, by converting the GMBE to a linear relationship between two parameter groups related with known formation/fluid properties and dynamic performance data, the straight-line reserve evaluation method is proposed. By using the slope and the y -intercept of this straight line, the original adsorbed gas in place (OAGIP), original free gas in place (OFGIP), original dissolved gas in place (ODGIP), and the original gas in place (OGIP) can be quickly calculated. Third, two validation cases for shale gas reservoir and CBM reservoir are conducted using commercial reservoir simulator and the coalbed methane dynamic performance analysis software, respectively. Finally, two field studies in the Fuling shale gas field and the Baode CBM field are presented. Results show that the GMBE and the corresponding straight-line reserve evaluation method are rational, accurate, and effective for both shale gas reservoirs and CBM reservoirs. More detailed information about reserves of shale gas and CBM reservoirs can be clarified, and only the straight-line fitting approach is used to determine all kinds of reserves without iteration, proving that the proposed method has great advantages compared with other current methods.

Pyrolysis kinetics and environmental risks of oil-based drill cuttings at China’s largest shale gas exploitation site

Chongqing Fuling shale gas field, the largest shale gas exploration site in China, produces a large amount of oil-based drill cuttings (OBDC) every year, which is a hazardous waste. Traditional treatment methods such as solidification/stabilization did not recycle the valuable components such as petroleum hydrocarbons. Pyrolysis is proven to be an efficient method that can recover those components. This study firstly investigated the pyrolysis kinetics by two different methods on the basis of detailed material characterization, and then taking the workers and the surrounding ecological environment as the analysis object, the human health risk assessment (HHRA) and ecological risk assessment were evaluated respectively before and after pyrolysis. The results showed that the pyrolysis of OBDC was divided into three stages, and the cracking of light hydrocarbons stage was the key control step for pyrolysis process. The activation energy E increased gradually during the pyrolysis progress. The HHRA results showed that pyrolysis could greatly reduce the non-carcinogenic risk, carcinogenic risk and ecological risk by 59.6 %, 62.8 % and 75 % respectively. However, the carcinogenic risk after pyrolysis was still higher than the critical value 10−6.

Shale gas wastewater geochemistry and impact on the quality of surface water in Sichuan Basin

Shale gas wastewater (SGW) disposal is a major challenge in the areas in central China due to its increasing volume associated with intensification of shale gas exploration and its high levels of contaminants. In the Fuling shale gas field of Sichuan Basin, a small amount of SGW originated from the flowback and produced water (FPW) is treated and then discharged to a local stream. This study investigated the inorganic water geochemistry and Sr isotopic composition of the FPW in Fuling shale gas field, the SGW effluent that is generated in the treatment facility, and the quality of a local river after the disposal of treated SGW. The data generated in this study reveals that FPW generate after several years of shale gas operation maintain the original geochemical fingerprints detected in early stages of FPW generation, and consistent with the FPW composition detected in other shale gas fields in Sichuan Basin. We show that reuse of saline FPW for hydraulic fracturing can generate an inverse salinity trend, where the salinity of FPW decreases with time, reflecting the increase of the contribution of formation water with lower salinity. The treatment of the FPW results in ~40 % reduction of the salts by dilution with freshwater and selective (80–90 %) removal of some of the inorganic contaminants. The original geochemical fingerprints of the FPW from Fuling shale gas field was not modified during FPW treatment, reinforcing the applicability of these tracers for detecting SGW in the environment. Discharge of treated SGW effluent to a local river causes a major 200-fold dilution and reduction of all contaminants levels below drinking water and ecological standards. Overall, this study emphasizes the importance of water quality monitoring of treated SGW and the overall measures needed to protect public health and the environment in areas of shale gas development.

A Shale Gas Leaking Incident in Fuling Shale Gas Field in Chongqing, China: A Case Study

A ground natural gas leaking event at the Fuling shale gas field is reported in this paper. Thirteen leakage spots were discovered in two places near the SW-1 and SW-2 drilling wells. The biggest leak rate was above 1000 m3 per day, and no H2S was identified in any of the 13 leaking spots, according to the field study. The chemical components, carbon isotope properties of the leaking gases, and the geological context of the leaking location were researched in order to determine the reason for the leaking incident. From the geological conditions, the Shimen 1# fault belt cuts the whole strata from bottom to top, according to seismic reverse time migration (RTM), and the fault and leaking spots are located in the range of the surface projection of the horizontal section of the adjacent shale gas well. The fracture development evaluation shows that the Wufeng–Longmaxi Formation, which is also the producing layer of the Fuling shale gas field, has a very high possibility of fracture development. From the geochemical view, the carbon isotope of the leaking gases lies in the range of the Wufeng–Longmaxi Formation, showing that the Wufeng–Longmaxi Formation is the gas source of the leaking gas.